1. Field of the Invention
This invention relates to a metallic mold for vulcanizing molding of a cogged V-belt of a raw edge type of a long length, particularly to an upper mold having a cogged surface with alternations of cog peaks and cog troughs.
2. Description of the Prior Art
In the vulcanizing molding of cogged V-belts of the raw edge type of a long length, a press vulcanizer using press metallic molds of a plate shape has been generally adopted. This press vulcanizer comprises a pair of pulleys adjustable in distance between the axes of the opposed pulleys and a press vulcanizing machine having an upper board (for surface side of belt), an intermediate board (for bottom side of belt) and a lower board (for downward surface side of belt), with a metallic mold of a plate shape on the belt support surface of each board. An unvulcanized belt material is wound round between a pair of pulleys and is moved in regular order for vulcanizing molding one part by one part.
When press vulcanizing molding is carried out by using a press metallic mold of a plate shape, it has been experienced that at the initial stage of vulcanization, rubber which is yet in semi-vulcanized state, namely, semi-vulcanized rubber near an end portion of the metallic mold flows out toward unvulcanized belt material positioned near the outside of the metallic mold, and as a result unvulcanized belt material positioned near the outside of the metallic mold is deformed and swelled into a bump shape, prior to vulcanizing molding, by being pressed by the flowing semi-vulcanized rubber.
If such a swelled part in a bump shape is vulcanizing molded as it is, with the arrangement of tension cords in disorder, an irregularity is caused in the thickness and width of the belt, and also in the cog shape. This poses a problem with respect to the quality of the cogged belt.
In view of the above demerits, it has been suggested by the Japanese Utility Model Registration Application Publication No. 1-23783, for example, to form a taper extending in such a fashion that it intersects perpendicularly the lengthwise direction at the edge part of the undersurface of both end portions (front end portion and rear end portion) of an upper board having a flat surface of a press metallic mold of a plate shape.
According to the above suggestion, a "taper escape" is provided at the back surface part of the belt, and therefore the incidence of extreme difference in level at the belt surface and irregularity of arrangement of tension cords and belt width will be small. However, a part of the rubber which forms cogs will flow toward the back part side of the belt, and as a result rubber for bonding tension cords (so-called insulation rubber) also presents a flowing phenomenon and is put in a bending state. This has a bad influence upon the adhesion between rubber and cords.
The volume of rubber required for forming a belt material must be the same as or larger than that of a finished belt (in the shape of a cavity of regular metallic mold), otherwise a finished belt of good quality cannot be obtained. If the volume of rubber for forming a belt material is less than that of a finished belt, the problem of "pinhole", "separation" or the like will be raised. Moreover, it is difficult to manufacture a belt material with rubber of the same volume as that of a finished belt. Thus, in manufacturing a belt material it is usual to use rubber of the volume which is larger than that of a finished belt, and accordingly it is unavoidable that a flowing phenomenon of rubber takes place.